Abstract:CZTSSe is an Earth-abundant, environmentally friendly, and low-cost material, with a current record power conversion efficiency of 14.9%, This result is well below the prediction of the Shockley-Queisser limit. To improve the performance of solar cells, a layer of PbS (BSF) was added to the CZTSSe, which was simulated using the SCAPS-1D software. The optimal photovoltaic performance of AZO/ZnO/CdS/CZTSSe/PbS/Mo was studied by changing the parameters of the CZTSSe absorption layer and PbS layer. Studies have shown that the efficiency can be increased to 20.86% after using PbS.